With the ever increasing number of telephone subscribers, continuous efforts have been made in the design of telephone connector blocks normally installed in telephone offices, to accommodate greater numbers of pin terminals per unit area. The increase in pin terminal density has been achieved to a considerable degree, but this desired result has also resulted in corresponding complication in the installation and maintenance of telephone circuits, owing to greater conductor density and more limited access space. Circuits are more difficult to trace, and because connector blocks are positioned very close to each other, it is necessary for service personnel to work with great care in order to avoid injury by contacting the exposed pins on the surface of an adjacent connector block. From the standpoint of simplifying service, little has been accomplished in the direction of protecting service personnel against injury, and in the area of facilitating circuit tracing.